Transport properties of amorphous silicon-germanium alloy films. Volume 2: Appendices

The basic optical and electrical properties of hydrogenated amorphous Si/sub x/Ge/sub 1-x/ alloy films in the range 0 less than or equal to x less than or equal to 0.46 were studied. The alloys were deposited by the plasma decomposition of silane-germane mixtures with doping performed by the introduction of AsH3,PH3 or B2H6 into the plasma. The interband absorption edge and temperature dependence of the dc conductivity were measured as functions of composition and doping level. The optical bandgap increases with Si content in accord with previous workers. This may or may not be a linear function. Substitutional doping of the amorphous alloys of both n- and p-type was achieved. Room temperature conductivity changes of three orders of magnitude were produced with gas phase doping levels of 500 vppM of B2H6 in 46% Si films. The corresponding change in activation energy is over 300 MeV. Contaminants, especially oxygen, appear to sharply reduce the doping efficiency of these alloys.